Abstract: The complex internal resonance mechanism for resistance-reducing by oscillation, fractal dimension of soil intensity and the characteristics of load signals are analyzed by means of soil bulk-subsoiler nonlinear system model developed by the author. The conclusions, to improve resistance-reducing capability in soil-tilling system by adjusting its natural frequency, and judge it by frequency-spectrum exponential of drag-resistance, are obtained. Meanwhile, these theoretical results are verified with the test data from field experiments.